The present invention relates, in general, to composite substrate such as headliners of motor vehicles, and in particular, to a new and useful process for bonding a cover and the substrate together.
U.S. Pat. Nos. 5,022,943 and 5,134,014, which are both incorporated here by reference, disclose methods, structures and materials for composite substrates of the type to which the present application relates.
FIG. 1 illustrates a corrugated fiberboard and thermoplastic composite substrate of the type which can be covered according to the process of the present invention.
The substrate generally designated 10 includes an upper kraft paper layer 12, and intermediate thermoplastic film layer 14 (e.g. PE), an inner kraft liner 16, an inner thermoplastic layer 18, and a corrugated fiberboard medium 20, with a similar construction opposite the corrugated medium.
FIG. 1 illustrates a single facer product while FIG. 2, where the same reference numerals are utilized to designate the same or similar elements, illustrates a single wall product. The combination of different paperweights with thermoplastic gives the substrate unique properties. When heat is applied, the films melt, releasing the liners and allowing the corrugated medium to slip into shape by using molding dies. After removing the heat, the thermoplastic films weld the materials together, rigidly in their new shape and configuration. The substrate is extremely versatile in its uses and the product can be laminated with different liner weights, PET, aluminum, non-woven or other materials bonded to the substrate for various applications. A vehicle headliner having various qualities of rigidity, noise absorption and other advantages is one example of a use for the substrate.
Two processes are currently known for manufacturing this type of composite substrate. FIG. 3 illustrates one of these processes in which one compression molding tool is used to both form and cover the substrate.
In an initial step 30, the substrate 10 is placed between an upper heated die 22 and a lower heated die 24, both heated to approximately 130.degree. C. In a subsequent pressure step 32, the dies are moved toward each other to heat and compress the substrate 10 for about 25-30 seconds.
In a subsequent step 34, the tool is opened by separating the dies 22, 24 from each other and a layer of cover material 40 is placed over the now formed substrate 10, between the dies.
Cover 40 may be any desired layer which is meant to be attached to either surface of the substrate 10, for an example, a decorative layer, with or without additional layers such as foam backings and the like. Examples of the types of cover layers which can be used are illustrated in U.S. Pat. No. 5,134,014. It is necessary that the cover layer 40 have a layer of heat activated adhesive or an adhesive quality or be capable of adhering under heating, to the substrate 10.
In subsequent step 36, the tool is closed by moving the dies 22, 24 toward each other to heat and apply pressure to the substrate 10 with cover 40, for an additional dwell time of approximately 25-30 seconds. Steps 32 and 36 represent first and second strokes for the tool. The second stroke 36 melts the adhesive on the cover material 40, bonding it to the substrate 10. The tool is then opened in step 38 and the molded substrate 10, 40, in the form of a vehicle headliner in the illustration of FIG. 3, is removed.
In a further step 42, the headliner 10, 40 is placed on a cooling nest 26. The cooled part may then be placed in a rack for later trimming or can be trimmed immediately in a subsequent trimming step. The process is then repeated for manufacturing additional products.
The advantages of this process are low cost since only one hydraulic press is required to open and close the tool. Good bonding is also achieved between the cover 40 and the substrate 10 because of the use of both upper and lower heated dies in the tool. In this field, the closing stroke 36 is referred to as a "heated marriage" step.
Disadvantages of the process illustrated in FIG. 3 include slow cycle time since two strokes are required in the same tool.
Since the substrate and perhaps even the cover have thermoplastic components, there is also the danger of deforming the product when it is removed from the heated tool. Care must be exercised, thus, in removing the product and this also involves additional time penalties.
Referring to FIG. 4, another known process for manufacturing the covered substrate, was developed to reduce cycle time and to yield a cool, easily handled part after the heated marriage of the cover material. In an initial step 50, substrate 10 is placed between heated dies of a first heated forming tool, heated to approximately 200.degree.-220.degree. C. In a second step 52 of the process, the tool is closed in a first stroke for approximately 25-30 seconds. In step 54 the tool is opened and the hot formed substrate 10 is placed between the cold dies 62 and 64 of a cold marriage tool. Cover material 40 is placed over the heated substrate 10 and the cold tool is closed in step 56.
The residual heat in the substrate 10 melts the adhesive of the cover material 40, thus bonding the cover to the substrate. While the marriage tool is cycling for approximately 25-30 seconds in its closed condition, another substrate can be molded in the hot forming tool 22, 24 thus increasing throughput, output or productivity.
In step 58, the cold marriage tool is opened and the cooled headliner 10, 40 can be removed for trimming or storage on a rack.
The advantage of the process of FIG. 4 is reduced cycle time. While the first substrate is in the cold marriage tool, another substrate can be running through the forming cycle. The thermoplastic is set, coming out of the cold marriage tool, allowing for immediate handling without the risk of deforming the product.
Disadvantages are that further reductions in cycle time are limited due to temperature requirements of the substrate when it is placed in the cold marriage tool. Occasional cover material de-lamination has also occurred when the substrate is too cool when it enters the cold marriage tool. Also, at forming temperatures over 220.degree. C. a noticable increase in odor occurs.
A need remains for further improvements in the manufacturing techniques of this type of covered composite substrate.